Communicating spring system with coned snap spring

ABSTRACT

A coned disc spring that is cocked overcenter has a keystone edge seated against a surface of a surrounding cylindrical support. In one embodiment, the support is a ring of softer material than the spring, and the keystone seat is formed by the spring being cocked. In such embodiment, the spring also functions as a diaphragm exposed to fluid pressure. At a predetermined pressure determined via adjusting means for setting its cocked position, the overcenter spring snaps and self-ejects from the ring.

United States Patent- Allen V. C. Davis Inventor 5600 Alta Canyada, La Canada, Calif. 9101 1 Appl. No. 791,903

Filed Jan. 17, 1969 Patented Jan. 19, 1971 COMMUNICATING SPRING SYSTEM WITH CONED SNAP SPRING 9 Claims, 13 Drawing Figs.

US. Cl. 220/89 Int. Cl 865d 47/36,

B6Sd 47/00 Field ofSearch 169/26, 31;

220/89, 47, 27; 267/l6l, 162, I63

[56] References Cited UNITED STATES PATENTS 1,774,946 9/1930 Rankin 220/ 89A l.775,028 9/1930 Hilliard 220/89A 3,464,585 9/ l 969 Summers 220/89A 3,467,120 9/1969 Hill et aI. 220/89A Primary Examiner-Raphael H. Schwartz Attorney-Perry E. Turner 1.01, i a I a 24 g; 30 J2 J6 20 E I 3! E js E 33 v the cylinder;

COMMUNICATING sriuNc svs raM WITI-I CONED SNAP SPRING BACKGROUND OF THE INVENTION pressure to operate a switch orto effect rupture of a thin diaphragm. Whatever the force needed tofactuate it, such a spring haslimited snap travel. Where it is desired to instantaneously propelparts through a substantial distance. such spring assemblies are incapable of fulfilling this need. Further. it has not heretofore been known to use such a spring as a sealing element or as an integral part of a communicating spring system.

SUMMARY OF THE lN'vENTloN My invention embraces a communicating spring system wherein the peripheral keystone'edge of 'a coned disc spring and a surrounding support element are in resilient engagement, and wherein the spring upon being snapped breaks the engagement and self-ejects from the space within the support elemenLElemcnts carried by the spring are ejected with it.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a longitudinal sectional vie'v'v of a pressure relief valve employinga communicating spring system of my invention;

FIG. 2 is a perspective view of a partof the valve of FIG. Ii

FIG. 3 is a fragmentary sectional view 'of the mating portions of the disc spring and surrounding ring preparatory to cocking the disc spring; l

FIG. 4 is a fragmentary sectional view like FIG. 3 but with the spring cocked, and wherein. due to the differential hardness between the spring and ring, the keystone is formed in the ring by the spring; V r 7 FIG. 5 is a fragmentary sectional view similar to FIG. 4, showing the ring with a modified keystone formed therein by the cocked spring; I 1 I k 1 FIG. 6 is a fragmentary sectional view like FIG. 4, showing a coating of plastic material on the top surfaces of the ring and sprang; r I

IFIG. 7 is a fragmentary sectional view of the parts of FIG. 6 immediately upon the spring snapping from overcenter;

FIG. 8 is a longitudinal sectional. view of a'pressure relief mechanism employing another communicating spring system' in accordance with my invention;

FIG. 9 is an enlarged, fragmentary sectional view of the mating surface portions of the spring and surrounding cylinder of FIG. 8, showing the keystone preformed in the cylinder;

FIG. 10 is an enlarged, fragmentary sectional view of the parts of FIG. 9, with the spring cocked so that its peripheral edge sealingly and resiliently engages the keystone surface in FIG. 11 is an enlarged, fragmentary sectional view of the cooperating parts'of the mechanism of FIG,'8, to illustrate limited movement of the center portion of the spring for permitting the integrity of the system to betested.

FIG. 12 is a fragmentary sectional view of parts being ejected upon the spring being released from overcenter; and

FIG. 13 is a graph of a load-deflection characteristic to aid in explaining the operation of my invention.

DESCRIPTION OF ILLUSTRAII'IVE EMBODIMENTS Referring to FIGS. 1 and 2, there is shown a pressure relief mechanism which includes a flanged body I0 having a central opening to be exposed to fluid pressure. In the arrangement shown, the lower end of the body 10 is provided with an annular shoulderabutted by the top surface of a ring 12 of a burst disc assembly 14..

As shown. the loading ring 16 is engaged by .an annular shoulder in the upper end of a rigid tubular element 18. The elem'entla is retained within a loading ring clamp 20. shown as a-rigid tubular element having an inwardly extending radial lip at its lower end to provide a ledge for an annular shoulder on the outer surface of the element I8. At its upper end. the

loading ring clamp 20 is threaded onto the flange of the body 10. As will be seen, the loading ring clamp 20 is threaded onto the body 10 tocause the ring 12, via thetubularelement l8 and the loading ring 16, to be securely and sealingly clamped against the body 10.

The burst disc assembly I4 is comprised of the ring 12; a

coned disc spring 24. a threaded rod'26 that is welded at its upper end to the spring 24; a stiff spring-engaging or backup plate 28 that is slidable on the rod 26; and a nut 30 threaded on the rod for engaging the plate 28. As will be noted. since the outer rim of the plate 28 engages aportion of the spring 24 between its center and rim, turning the nut 30 against the plate 28 adjusts the height of the spring 24. l v

In accordance with my invention, the spring 24 and ring 12 form a communicating spring system wherein the peripheral edge of the. spring 24 is in face-to-face contact with the ring 12.?Ihe ring 12 exerts a compressive force on the peripheral edge of the spring 24; and is in turn subjected to a hoop stress. Due to the interacting spring forces between the spring 24 and the ring 12, their contacting surfaces effectively form a seal against leakage of fluid to'which the upper end of the body 10 is exposed. 1

Further, the spring 24 is cocked overcenter, to an extent determined by the adjusting means 26, 28, 30. The overcenter.

. spring is releasedupon the fluid pressure above the spring 24 reaching a predetermined level, and the ensuing snap action ejects the spring 24, together with the rod 26, plate 28 and nut 30, toward the lower end of the tubular element 18.

The tubular element 18 formspart'of a retainer assembly. In this connection, aweb or spider 34 is supported adjacent the open' end of the element 18. In the particular arrangement shown, the spider 34 is formed of weldedplates 36 shaped to provide a central opening 38. Thelegs of the spider 34 are shown with finger extensions captured in an annular groove in the open end of the element I8. I

The tubular element 18 and spider 34 provide a retainer means to catch the ejected parts. The diameter of the opening 38 is larger than that of the nut 30. When the spring 24 snaps from over center to cause ejection, the rod 26 passes through the opening 38, and the nut 30 enters the opening. Since the plate 28 is slidable on the rod 26, it comes to rest on the top of a washer 40 on the spider. and the flangedupper end of the rod 26comes to rest on the upper surface of the plate 28. The snapped spring 24, of course, is carried with the rod.

As will now be apparent, ejection of the parts above described results in a pressure relief path around the edge of the snapped spring 24 and through the spaces between the legs of the spider 34 and out of the lower end of the tubular element I8.

It should be noted that my invention may be employed in a variety of forms of pressure relief. mechanisms. For example, the retainer means could be eliminated, to permit the ejected parts to be blown out of the lower end of the tubular element 18. Alternatively, the lower end of the tubular element could be closed, in which case the ejected parts are thrust against such closed erld. Also in such case,.openings are provided in the skirts of the elements 18, 20 to provide appropriate pressure relief passages to the atmosphereIIn this latter arrangement, the rod 26 is substantially shortened.

FIGS. 3-5 illustrate how the spring and keystone ring are assembled to form the communicating spring system abovedescribed. In FIG.'3, the spring 24 is shown in its uncocked condition. The edge surface of the spring is shaped so that, in the uncooked condition, it is parallel to the surrounding cylindricalface of the ring 12. A stop member, shown in phantom at 42 in FIG. 3, is positioned on top of the ring 12. The uncocked spring is moved in sliding engagement with the inner cylindrical surface of the ring 12 until it abuts the stop member 42. The center portion of the spring is then thrust upward to be cocked overcenter. The diameter of the spring increases as it is being cocked, and tends to spread the ring. Accordingly, it is preferred to apply a radial compressive force to the outer face of the ring while the spring is being cocked.

The ring 12 has a keystone bearing surface for the peripheral edge surface of the spring 24. In this connection, my invention embraces a spring and keystone ring characterized by differential hardnesses. In one arrangement, the spring is of stainless steel and the ring is of aluminum. In such arrangement, as best seen in FIG. 4, the harder spring material bites into the ring 12 as the spring is cocked, and thereby forms the keystone surface in the ring. As will be seen, the spring and ring could be of the same material, and the keystone surface could be preformed in the ring.

FIG. 5 illustrates an arrangement wherein the ring forms a smaller keystone surface in the ring, i.e., wherein the bearing surface portions of the ring and spring extend only a short distance below their upper surfaces. Also illustrated in FIG. 5 is the small diameter change occasioned by the outward radial force exerted by the spring on an uncompressed ring. This further illustrates the communicating or interacting spring system formed by the ring and the spring.

FIG. 6 illustrates a further refinement of the assembled communicating spring system of my invention. After the spring 24 is cocked as above-described, a thin layer 46 of material, e.g., plastic, is coated on and spans the upper surfaces of the spring 24 and the ring 12. The coating 46 may be of any desired nonporous material. The coating is quite thin, e.g., teflon coatings from .001 inch.002 inch thickness on disc springs of thicknesses in the neighborhood of .016 inch- .020 inch. Such a resilient plastic coating provides a leakproof seal along the shoulder of the body against which the coating 46 is pressed.

FIG. 7 illustrates the assembly of FIG. 6 upon the spring being released from overcenter. As shown, the snap movement of the spring causes the coating 46 to be broken, whereupon the spring and parts movable therewith are ejected from within the ring 12.

FIG. 8 illustrates another embodiment of the communicating spring system of my invention. In this embodiment, the communicating spring system is also in a burst disc assembly that includes a coned disc spring and a surrounding keystone element with interacting spring forces. The coned disc spring is shown at 50 with its peripheral edge seated on a keystone surface that is preformed in a surrounding thin-walled cylindrical element 52.

In the arrangement shown, the cylindrical element 52 has a thick wall portion at its upper end which is threaded onto a body 54 having an opening to be exposed to fluid pressure, e.g., via an inlet tube 56 welded to a ring 58 that is in turn welded to the body 54. The spring 50 in this embodiment has a central opening, and the inner peripheral edge thereof is locked to the lower end ofa backup plate 60 that is slidable in a ring 62. A diaphragm 64 spans the opening in the body 54, and extends between the lower end of the body and the ring 62. As indicated, the ring 62, diaphragm 64 and body 54 are welded together.

In the assembly of the above-described structure, and referring to FIGS. 9 and 10 along with FIG. 8, the lower thin-walled portion of the element 52 has an upwardly diverging groove 66 formed therein to provide the keystone seat for the peripheral edge of the spring 50. Further, the portion of the element 52 below the groove 66 is of slightly larger diameter than the portion thereof above the groove.

As in the preceding example, the peripheral edge of the spring 50 is shaped so that in its unflexed condition, its edge surface is parallel with the surrounding cylindrical surface of the element 52 (see FIG. 9). In its unflexed condition. the spring is inserted in the lower end of the element 52 and moved upwardly therein with its peripheral surface, slidably engaging the surrounding wall of the element 52. The upper edge of the spring engages the shoulder formed by the reduced diameter section of the element 52 above the groove 66, so that further movement of the center of the spring causes it to be cocked overcenter and forces its peripheral surface into firm metal-to-metal contact with the keystone seat (FIG. 10).

It will be understood that the spring 50 and backup plate 60 have been previously assembled. This is done by sliding the center portion of the spring over the lower end of the backup plate, and then spinning over the-lowerend of the backup plate to capture the spring. g p

The wall of the lower end of the=cylindrical element 52 is purposely made sufficiently thin to insuriathat both the spring 50 and such thin wall provide interacting spring forces. Where such wall is so thin around the keystone groove 66 that it might fail under the hoop stress exerted by the spring 50, the element 52 is formed with a reinforcing rib around the keystone.

As shown, the backup plate 60 enters the ring 62 when the spring 50 is cocked as above-described. The backup plate has an annular shoulder that engages the bottom surface of the ring 62, i.e., the ring forms a stop for the upper position of the backup plate. In such upper position, the top surface of the backup plate engages the bottom of the thin diaphragm 64. Further, with the backup plate in such upper position. the cocked condition of the spring 50 is adjusted as desired by appropriately adjusting the position of the cylindrical element 52 on the body 54, whereupon the position of the element 52 can be fixed, as by a set screw 72.

With the arrangement thus far described, when pressure on the diaphragm 64 above a predetermined level causes the backup plate 60 to move down sufficiently to release the spring 50 from overcenter, the spring and backup plate are snap-ejected out of the cylindrical element 52. Accordingly, the excessive pressure will rupture the diaphragm.

Diaphragm rupture canbe enhanced by suitable cutting means. In the arrangement shown, a cutter element 76 is placed on top of the diaphragm 64. The cutter, diaphragm and backup'plate are spot-welded together. Thus, when the spring and backup plate are snap-ejected out of the cylindrical element 52, the cutter 76 is carried with them, together with the portion of the diaphragm that is bounded by the cutting edge of the 'cutterI The cutter may have a cutting edge of any desired contour, e.g., as in any of the well-known household cooky cutter.

In the arrangement thus far described, the ejected parts are simply blown out of the lower end of the cylindrical element 52. However, the parts preferably are captured by suitable retaining means. In this regard, there is shown a housing formed of the body 54, a sleeve 80 welded at its upper end to the body, and a cylindrical block 82 to which the lower end of the sleeve 80 is welded. The block 82 has a central opening that serves as a pressure outlet port.

When the associated parts are ejected as above-described, they are prevented from passing into and blocking the outlet port 84. In the illustrated arrangement, this is achieved by means ofa screen 86 spanning the port at the top of the block 82, and a plurality of spaced vertical pins 88, here shown supported in a ring that sets on the screen and is welded to the upper surface of the block 82. The upper ends of the pins 88 are sufficiently spaced above the ring 90 to insure that the ejected parts cannot block the port 84, and to insure a pressure relief path around the periphery of the spring 50 and between the pins 88'to the port 84.

Further explanation of the operation of the burst disc assemblies above-described will be made with reference to FIG. 13. FIG. 13 is a graph of a load deflection characteristic of a coned disc spring suitable for use as above-described. The origin of the graph represents the unflexed condition of the spring. The positive portion of the curve illustrates the loaddeflection variations as the body of the spring is flexed to snap through the center, or nearly flat, condition, indicated at 92.

The negative portion of the characteristic represents the over- In this latter connection. I prefer to adjust the spring so that its overcenter position is on the decreasing slope of the negative portion of the characteristic. In FIG. 13-. the point 94 illustrates the position at which the spring is held or cocked. When sufficient pressure is applied to move the spring from this stop position, the spring does not return directly along its negative characteristic. Rather, as indicated b y the arrow, the spring in moving from such stop position 94 exhibits a positive spring rate, following which it snap deflects from overcenter to it unflexed condition. t

Such positive-to-negative snap deflection may take place from any of a variety of positions as determined by the adjusting means previously described. However, the preferred arrangement, in which the overcenter position of the spring is set on the decreasing slope of the negative portion of the load deflection characteristic, is calculated to provide the'spring system with optimum sensitivity. Thus, the system may be adjusted so that a single pulse of fluid pressure above a predetermined level is effective to cause the abovewdescribed ejection of the coned disc spring and parts connected thereto.

FIGS. 8 and ll also illustrate testing "means which may be employed to provide information that the spring system is intact and operative for the desired purposes. As shown in FIG. 8, a pair of arms 100 are secured at their upper ends to the spring 50, and the lower ends of thearms support electrical contacts I02. In the cocked condition of the spring 50, the lower ends of the arms are positioned so that the contacts 102 are in engagement.

As shown, the respective contacts 102 are connected to a test circuit;l04. Extremely slight downward movement-of the spring 50 causes the lower ends of the arms [00 to spread, thereby breaking'the connection between the contacts 102. When this occurs, the test circuit 104 provides anindication. e.g., extinguishment of a lamp (not shown) which is illuminated while the contacts 102 are in engagement. If desired, of course, the circuit may be arranged to illuminate a lamp when the contacts 102 are broken.

As will be seen with reference to FIG. 13, the abovedescribed testing is effected without causing the spring 50 to snap from overcenter, i.e., movement is confined to the positive portion of the positive-to-negative snap deflection charac' teristic above described. j

As will be apparent, testing means as above described can readily be adapted for the burst disc assembly shown in FIG. 1. Further, it will be apparent that my invention embraces other suitable means for checking the .condition of the spring system.

lclaim:

1. In combination:

a spring support element having a cylindrical wall;

a coned disc spring coaxial with said wall, said disc spring being positioned with itsperipheral edge surrounded by and bearing against said wall;

said disc spring being cocked overcenter with said peripheral edge exerting outward radial force against said wall, whereby said spring support element is subjected to a hoop stress and exerts counteracting inward radial force against said peripheral edge, the counteracting radial forces'of said disc spring and, spring support element being effective to maintain the peripheral edge of said cocked discspring firmly engaging said wall in the absence of a predetermined forceapplied axially to the convex side of said disc spring in a direction to cause it to snap from overcenter, said counteracting forces combining upon application to said disc spring of a predetermined axial force to assist said peripheral edge to break away from its cngagement with said wall and cause said disc spring to selfeject from within said spring support element;

and means for selectively adjusting the extent to which said disc spring is cocked overcenter. whereby to selectively determine the axial force needed to cause said disc spring to snap from overcenter and self-eject from within said spring sup rt element. 2.. he com matron of claim 1, wherein said support element has a keystone formed in said wall. and wherein the peripheral edge of said disc spring engages said keystone.

3. The combination of claim 2. wherein said disc spring is of material that is harder than the material of said wall. and 5 wherein the peripheral edge of said disc spring forms the keystone in said wall when said disc spring is cocked overcenter.

4. The combination of claim 3, wherein said spring support element is a ring; a conduit to be exposed to fluid pressure at one end; and means securing said ring to said conduit with said disc spring positioned to be snapped from overcenter upon fluid pressure in said one end of said conduit reaching a level to exert said predetermined force on said disc spring.

5. The combination of claim 4, wherein said conduit has an annular shoulder downstream from said one end thereof, said securing means holding said ring with one surface thereof resilient material on said ring sealingly engaging said annular shoulder, the portion of said coating of resilient material on said disc spring being severed from the portion thereof on said ring when said disc spring snaps from overcenter. 7. The combination of claim 1, including a conduit to be exposed to fluid pressure at one end;

a diaphragm extending across said conduit and secured thereto downstream from said one end thereof;

a ring abutting and secured to said conduit and to the downstream edge surface portion of said diaphragm;

a plate slidable in said ring and having an annular shoulder abutting the downstream edge surface of said ring;

and said spring support element being a cylindrical element threaded onto said conduit;

said disc spring being downstream of said plate;

and said plate being attached to and carried by the upstream center'portion of said disc spring.

8. The combination of claim I. wherein said adjusting means includes a rod welded at one end to the center portion of the concave side of said disc spring;

a backup plate slidable on said rod to bear against the con cave side of said disc spring;

and a nut element threaded on said.

position of said plate to determine the height of said over center disc spring.

9. The combination of claim 7. further including a cutter element secured to the upstream .surface of said diaphragm; and said cutter element, diaphragm and plate being secured together; said cutter element being dimensioned to pass through said ring when upon said disc spring being snapped 5 from overcenter.

rod for adjusting the. 

1. In combination: a spring support element having a cylindrical wall; a coned disc spring coaxial with said wall, said disc spring being positioned with its peripheral edge surrounded by and bearing against said wall; said disc spring being cocked overcenter with said peripheral edge exerting outward radial force against said wall, whereby said spring support element is subjected to a hoop stress and exerts counteracting inward radial force against said peripheral edge, the counteracting radial forces of said disc spring and spring support element being effective to maintain the peripheral edge of said cocked disc spring firmly engaging said wall in the absence of a predetermined force applied axially to the convex side of said disc spring in a direction to cause it to snap from overcenter, said counteracting forces combining upon application to said disc spring of a predetermined axial force to assist said peripheral edge to break away from its engagement with said wall and cause said disc spring to self-eject from within said spring support element; and means for selectively adjusting the extent to which said disc spring is cocked overcenter, whereby to selectively determine the axial force needed to cause said disc spring to snap from overcenter and self-eject from within said spring support element.
 2. The combination of claim 1, wherein said support element has a keystone formed in said wall, and wherein the peripheral edge of said disc spring engages said keystone.
 3. The combination of claim 2, wherein said disc spring is of material that is harder than the material of said wall, and wherein the peripheral edge of said disc spring forms the keystone in said wall when said disc spring is cocked overcenter.
 4. The combination of claim 3, wherein said spring support element is a ring; a conduit to be exposed to fluid pressure at one end; and means securing said ring to said conduit with said disc spring positioned to be snapped from overcenter upon fluid pressure in said one end of said conduit reaching a level to exert said predetermined force on said disc spring.
 5. The combination of claim 4, wherein said conduit has an annular shoulder downstream from said one end thereof, said securing means holding said ring with one surface thereof bearing against said shoulder.
 6. The combination of claim 4, wherein: said conduit has an annular shoulder downstream from said one end thereof; and an unbroken coating of resilient material covering the upstream surfaces of said disc spring and ring; said securing means holding said ring with a portion of said coating of resilient material on said ring sealingly engaging said annular shoulder, the portion of said coating of resilient material on said disc spring being severed from the portion thereof on said ring when said disc spring snaps from overcenter.
 7. The combination of claim 1, including a conduit to be exposed to fluid pressure at one end; a diaphragm extending across said conduit and secured thereto downstream from said one end thereof; a ring abutting and secured to said conduit and to the downstream edge surface portion of said diaphragm; a plate slidable in said ring and having an annular shoulder abutting the downstream edge surface of said ring; and said spring support element being a cylindrical element threaded onto said conduit; said disc spring being downstream of said plate; and said plate being attached to and carried by the upstream center portion of said disc spring.
 8. The combination of claim 1, wherein said adjusting means includes a rod welded at one end to the center portion of the concave side of said disc spring; a backup plate slidable on said rod to bear against the concave side of said disc spring; aNd a nut element threaded on said rod for adjusting the position of said plate to determine the height of said overcenter disc spring.
 9. The combination of claim 7, further including a cutter element secured to the upstream surface of said diaphragm; and said cutter element, diaphragm and plate being secured together; said cutter element being dimensioned to pass through said ring when upon said disc spring being snapped from overcenter. 